linux-kernel - Re: [PATCH 2/5] gpio: Cygnus: add GPIO driver

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Message-ID: <1417833291.31745.5.camel@perches.com>
Date:	Fri, 05 Dec 2014 18:34:51 -0800
From:	Joe Perches <joe@...ches.com>
To:	Ray Jui <rjui@...adcom.com>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Christian Daudt <bcm@...thebug.org>,
	Matt Porter <mporter@...aro.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Scott Branden <sbranden@...adcom.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-gpio@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 2/5] gpio: Cygnus: add GPIO driver

On Fri, 2014-12-05 at 18:14 -0800, Ray Jui wrote:
> On 12/5/2014 5:28 PM, Joe Perches wrote:
> > On Fri, 2014-12-05 at 16:40 -0800, Ray Jui wrote:
> >> +static void bcm_cygnus_gpio_irq_handler(unsigned int irq,
> >> +		struct irq_desc *desc)
> >> +{
> >> +	struct bcm_cygnus_gpio *cygnus_gpio;
> >> +	struct irq_chip *chip = irq_desc_get_chip(desc);
> >> +	int i, bit;
> >> +
> >> +	chained_irq_enter(chip, desc);
> >> +
> >> +	cygnus_gpio = irq_get_handler_data(irq);
> >> +
> >> +	/* go through the entire GPIO banks and handle all interrupts */
> >> +	for (i = 0; i < cygnus_gpio->num_banks; i++) {
> >> +		unsigned long val = readl(cygnus_gpio->base +
> >> +				(i * GPIO_BANK_SIZE) +
> >> +				CYGNUS_GPIO_INT_MSTAT_OFFSET);
> >> +		if (val) {
> >
> > This if (val) and indentation isn't really necessary
> >
> 
> Note for_each_set_bit in this case iterates 32 times searching for bits 
> that are set.

No it doesn't.

#define for_each_set_bit(bit, addr, size) \
	for ((bit) = find_first_bit((addr), (size));		\
	     (bit) < (size);					\
	     (bit) = find_next_bit((addr), (size), (bit) + 1))

find_first_bit:

 * Returns the bit number of the first set bit.
 * If no bits are set, returns @size.

>  By having the if (val) check here, it can potentially save 
> some of such processing in the ISR. I agree with you that it introduces 
> one extra indent here but I think it's required.
> 
> >> +			for_each_set_bit(bit, &val, 32) {
> >
> > for_each_set_bit will effectively do the if above.
> >
> > 32 bit only code?
> > otherwise isn't this endian unsafe?
> >
> 
> Will change 'unsigned long val' to 'u32 val'.

All the bit operations only work on long *


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